High frequency electrical apparatus



may 22 W56 i.. TONKS HIGH FREQUENCY ELECTRICAL APPARATUS Filed May l2,1945 Figi,

mvmnor HiG-i FREQUENCY ELECTRICAL APPARATUS )Lewi Tonks, Schenectady, NuY., assigner to General Electric Company, a corporation of New YorkApplication May l2, 1945, Serial No. 593,493

9 Claims. (Cl. 315-39) My invention relates to high frequency electricalapparatus and more particularly to an improved high frequency couplingfor connecting a concentric type transmission line with a resonantstructure. While not limited thereto, the coupling of my invention iswell adapted for tuning or suscep'tance controlling systems for highfrequency electric discharge devices of the magnetron type.

A large number of tuning arrangements have been employed for controllingthe frequency of electric discharge devices of the type employing aspace resonant structure. For example, in magnetrons employing a spaceresonant anode structure a large variety of mechanical tuningarrangements have been employed in which a disk or other tuningstructure is moved relative to the anode to control the operatingfrequency of the device. In other arrangements, a concentrictransmission line has been coupled to the resonant anode and the lengthof the line controlled to vary the operating frequency of the magnetron.In known arrangements of the latter type the coupling with the anode hasbeen such that unwanted impedances and voltages have appeared in the'resonant circuits of the anode and the mechanical movements requiredfor tuning the line have been relatively large.

ln accordance with the teachings of my invention, I provide an improvedtuning or impedance controlling arrangement particularly in combinationwith a resonant anode structure which provides a wide variation insusceptance with a relatively simple mechanism requiring movements ofsmall magnitude.

lt is an object of my invention to provide a new and improved impedancecontrolling or tuning system for high frequency electrical apparatus.

lt is another object of my invention to provide a new and improvedcoupling between a resonant anode structure and a transmission line ofthe concentric type.

In accordance with the illustrated embodiment of my invention, theoperating frequency of a magnetron of the radial vane type is controlledby controlling the susceptance between the straps which conductivelyconnect alternate vanes. The susceptance is controlled by a transmissionline of the concentric type having the outer conductor formed as part ofone of the vanes of the magnetron and the inner conductor connected withthe strap associated with the vanes not directly connected through thestraps with the outer conductor. The transmission line includes asection having a progressively varying characteristic impedance which isterminated by an adjustable capacitor formed by a plate carried by theend of the central conductor and a co-operating plate carried by adiaphragm secured to the outer conductor. The value of capacitanceintroduced is adjusted so that at a frequency at some mean of thefrequency range of operation desired, the susceptance reflected at theanode straps is zero. This frequency will be called the untunedfrequency. Physically, the length of line is less than one-halfwavelength at the untuned frequency by an amount determined by themagnitude of the capacitance introduced by the terminal plates. in otherwords, the concentric line is equivalent to a half ice wavelengthopen-ended line with this adjustment of the terminating capacitor. Asthe capacity at the end of the line is increased by decreasing the gapbetween the plates, the susceptance at the straps is capacitive and theresonant anode structure is tuned to a lower operating frequency. In asimilar manner, by moving the plate in the opposite direction todecrease the capacitance terminating the line, the susceptance at thestraps is effectively inductive and the anode structure is tuned to ahigher operating frequency. By utilizing a section of transmission lineof increasing characteristic impedance with distance from the straps, amultiplication in the susceptance change at the straps as compared withthe susceptance change at the end of the line is obtained. By formingthe outer conductor of the transmission line as a portion of one of theanode sections, the inner conductor is completely shielded fromelectromagnetic iields in the region above and below the anode so thatunwanted voltages and impedances are not introduced between the strapsof the anode.

In the copending Piske and Nelson application Ser. No. 593,492, tiledconcurrently herewith (now Patent 2,523,286, dated September 26, 1950),is described and claimed a frequency control system in which a tunableresonator is coupled by a transmission line to an oscillator,

such as the resonant anode structure of a magnetron. The

disclosure of the Fiske and Nelson application is prior art with respectto my invention.

My invention will be better understood by reference to the followingdescription taken in connection with the accompanying drawing in whichFig. l is an elevational View, partially in section, of a tunablemagnetron embodying my invention, and Fig. 2 is a plan View, partiallyin section, of the arrangement shown in Fig. l.

Referring now to the drawing, the magnetron device includes a generallycylindrical envelope l which is formed of material, at least the surfaceportion of which possesses good electrical conductivity. The spaceresonant anode structure of the device includes a plurality of vanes 2extending radially from the side wall of the envelope ll and terminatingshort of the axis of the envelope to provide a generally cylindricalspace 3 for the reception of a cathode 4. The cathode is generallycylindrical in shape and is provided at its ends with circular endplates or shields 5 and 6 which in the particular form illustrated areformed 5 as an integral part of the cathode. The cathode 4 is supportedby a tubular support 7 extending through an open- `ing in the cover ofthe envelope and secured in vacuumtight relation to the upper end of asleeve 8. The sleeve 8 is in turn supported from the cover of theenvelope by a cylindrical and vacuum tight insulator 9 and a sleeveterminal of a heater element (not shown).

lil which is welded to the cover about the opening through which thetubular support 7 extends. The portion l1 of the support 7 extendingbeyond the sleeve 8 may be employed as an external connection for thecathode and one The other supply terminal for the heater element isprovided by a conductor 12. sealed through the end of the support 7 by abody of glass 13 and maintained in spaced relation with the interior ofthe tube 7 by one or more spacing insulators 14.

In order to improve the stability of operation of the magnetron in thedesired mode, the two sets of alternate vanes are conductively connectedtogether by conducting rings l5 and lo, respectively, which are screwedor otherwise secured to the edges of the vanes 2 at the region adjacentthe inner ends thereof. As illustrated in the drawing, each vane isrecessed at 17 to receive one strap in contact with the walls of therecess and the other strap in spaced relation with the walls of therecess. As

appears from Fig. 2 of the drawing, the recesses in alternate vanes arearranged in reverse relationship so that the straps are conductivelyconnected only with alternate vanes. The straps 15 and 16 may beprovided at both ends of the anode structure as shown in Fig. 1.

In accordance with an important aspect of my invention, the susceptancebetween the straps l5 and i6, and as a result the operating frequency ofthe magnetron, is controlled by a tuning system including a transmissionline of the concentric type having an outer conductor 1% and an innerconductor` i9. The outer conductor 1S extends through the wall of theenvelope i in alinement with one of the vanes 2 which is recessed at itsupper portion to receive the conductor which is secured in position bybrazing or otherwise bonding to the envelope i and the recessed vane 2.The outer conductor thus forms a portion of the vane 2 and, asillustrated, terminates at its inner end at approximately the outer edgeof the inner strap 16. Thus the outer conductor is directly connectedwith the alternate anode sections which are connected by strap 16. Theinner conductor is secured to strap 3.5' in any suitable manner, as by ascrew 2@ and brazing, and is thus connected to the remaining anodesections. Alternatively, the outer conductor i8 may be made a part ofone of the vanes connected to the outer strap l5. In that case, theinner conductor would be connected to the inner strap 16. The portion ofthe transmission line outside of the casing includes a section of outerconductor 2l of progressively increasing diameter and a section of innerconductor 22 of progressively decreasing diameter. The inner conductormay be maintained in position by a spring lock 22 of insulatinrymaterial as illustrated in Fig. l. lt will be apparent that in thearrangement illustrated the ratio of the outside diameter to the insidediameter increases progressively and that the characteristic impedancetherefore increases progressively from the small end of the flaredportion 2l to the end of the line. The outer end of the inner conductor22 terminates in a disk-like member 23 which cooperates with a similardisk-shaped member 24 carried by a iiexible diaphragm or reflector 25 toterminate the line with an adjustable capacitor. The diaphragm orreiiector 25 is connected with and supported from the outer conductor 2lby an end wall or header 26 which is received in and welded, orotherwise bonded, to the outer conductor 2i. The movable disk member 24is operated from an external thumb cap 27 by an operating rod 2S havingits inner end secured to the disk 24 and its outer end rotatablyreceived in the thumb cap 27. The cap engages a threaded sleeve 29secured to the header 26 so that rotation of the cap 27 is eiiective tomove the disk 24 axially with respect to the fixed elements of thetransmission line.

The transmission line is sealed by a bellows 30 surroundy ing theoperating rod 28 and bonded to the header 26 and a iiange 3i on theouter end of the operating rod 2S.

Any suitable output connection for extracting energy from the resonantanode structure may be provided. As illustrated in the drawing, theoutput circuit is in the form of a concentric line having an outerconductor 32 secured to the side wall of the envelope i and an innerconductor 33 sealed through the envelope by a body of glass 3ft joiningthe inner and outer conductors 32 and 33. The inner end of conductor 33(not shown) is connected directly to one of the radial vanes 2. it willbe understood that suitable permanent magnet or electromagnet means willbe employed for producing a magnetic eld in an axial direction in theinterelectrode space. The field may be in the direction of the arrow inFig. l.

In the operation of the illustrated embodiment of the inventionelectrons emitted from the cathode d move in curvilinear paths in thespace between the cathode and the ends of vanes 2 under the combinedaction of an axial magnetic eld and a radial electric field produced bya Joitage impressed between the anode and the cathode Ai. The path ofthe electrons is also determined by the geometry of the anode structure.As the electrons move past the gaps between the ends of the vanes 2, theanode structure is excited into high frequency oscillation. The

transmission line system connected with the straps l5 and 16 is designedso that for an intermediate value of operating frequency, namely theuntuned frequency, the disk 24 occupies an intermediate position and thesusceptance between the two sets of alternate anode sections connectedby straps i5 and le, respectively, is Zero. As the disk 24 is movedtoward the disk 23, the capacity terminating the line is increased withthe result that a capacitive susceptance appears between the straps i5and i6 thus tuning the device to a lower operating frequency.Conversely, as the tuning disk 2d is moved from its intermediateposition away from the tuning disk 23, an effective inductivesusceptance is connected between the straps l5 and 16 and the device istuned to a higher operating frequency. Since the characteristicimpedance of the tapered section of the transmission line increasesprogressively as the ratio of the outside diameter to the insidediameter increases, it will be apparent that the adjustable capacity isat the end of the line having a high value of characteristic impedance.With this arrangement a small change in the susceptance at the outer endof the line is reflected as a larger change in susceptance betweenstraps i5 and i6, thus rendering it possible to effect a large range oftuning of the device with a relatively small change in capacitance atthe end of the line. The arrangement of the inner end of the outerconductor of transmission line as a part of the anode structure has alsobeen found very effective in eliminating unwanted impedances andvoltages in the tuning system. lt will be apparent that this feature isapplicable to a concentric line coupled with a resonant anode structure,whether the line forms a part of a tuning system or simply a part of anoutput system.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that changesand modications may be made without departing from my invention in itsbroader aspects, and l, therefore, aim in the appended claims to coverall such changes and modiiications as fall within the true spirit andscope of my invention.

What l claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A tuning device for high frequency electrical apparatus comprising, aconcentric transmission line including inner and outer conductors andhaving a portion the characteristic impedance of which increasesprogressively with 'the length of the line, an adjustable capacitor andmeans constituting a reilector terminating said line at the end thereofhaving the higher characteristic impedance, and means connected to saiddevice for adjusting the magnitude of said capacitor to produce amultiplied change in susceptance at the other end ot said line.

2. A tuning device for high frequency electrical apparatus comprising, alength of concentric-type transmission line including inner and outerconductors, said transmission line including a section in which theratio of the diameter of the outer conductor to the diameter of theinner conductor increases progressively, a disk-like member terminatingthe inner conductor, a I.2o-operating disklike member electricallyconnected with the outer conductor by a reiiector means and mounted inopposed relation to said rst mentioned disk-Eike member, and meansattached to said device for adjusting said second disk-like member tocontrol the susceptance at the other end of said transmission line.

3. A high frequency electric discharge device of the magnetron typecomprising, a generally cylindrical anode structure having a pluralityof spaced radially extending anode sections defining a plurality ofcoupled resonant circuits, conducting means connecting alternate anodesections together, a transmission line of the concentric type having theouter conductor thereof formed as a portion of one of said anodesections and the inner conductor connected with adjacent anode sectionsby said conducting means, and means terminating said line at the endremote from said anode sections for adjusting the effective length ofsaid transmission line to control the operating frequency of saiddevice.

4. A high frequency electric discharge device of the magnetron typecomprising, a generally cylindrical anode structure having a pluralityof spaced radially extending anode sections defining a plurality ofspaced resonators, conducting means connecting alternate anode sectionstogether, a transmission line of the concentric type having the outerconductor thereof formed as a portion of one of said anode sections andthe inner conductor connected with the other set of alternate anodesections, said transmission line including a section in which the ratioof the diameter of the outer conductor to the diameter of the innerconductor increases progressively, and adjustable capacitance meansterminating said line at the end transmission line section at which saidratio is larger.

5. A high frequency electric discharge device of the magnetron typecomprising, an anode structure including a plurality of mutually spacedanode sections defining a plurality of cavity resonators, conductingmeans connecting alternate anode sections together, a transmission lineof the concentric type having the outer conductor thereof formed as aportion of one of said anode sections and the inner conductor connectedwith adjacent anode sections by said conducting means.

6. A high frequency electric discharge device of the magnetron typecomprising a generally cylindrical anode structure having a plurality ofradially extending anode sections defining a plurality of cavityresonators and a transmission line of the concentric type includinginner and outer conductors, said transmission line being mounted withthe conductors thereof extending in the direction of one of said anodesections and with the outer conductor formed as a part or said onesection, said conductor extending snbstantially to the inner end of saidsection, and means connecting the other of said conductors with an anodesection adjacent said one section.

7. A high frequency electric discharge device of the magnetron typecomprising a generally cylindrical anode structure having a plurality ofradially extending anode sections defining a plurality of cavityresonators and a transmission line of the concentric type includinginner and outer conductors, said transmission line being mounted withthe conductors thereof extending in the direction of one of said anodesections and with the outer conductor formed as a part of said onesection, said conductor extending substantially to the inner end of saidone section.

8. A high frequency electric discharge device of the magnetron typecomprising a generally cylindrical anode structure having a plurality ofradially extending anode sections defining a plurality of cavityresonators, and a transmission line of the concentric type includinginner and outer conductors, said. transmission line hein g mounted withthe conductors thereof extending in the direction of one of said anodesections and with one of the conductors formed as a part of said onesection, said one anode section and said one conductor being similar tothe remaining anode sections and said conductor extending substantiallyto the inner end of said section, and means connecting the other of saidconductors with an anode section adjacent said one section near theinner end thereof.

9. A tunable radio frequency generator comprising a magnetron, saidmagnetron having a plurality of individual cavity resonators havinginner open ends, a coaxial transmission line having a portion externalsaid magnetron and having a portion within said magnetron terminatingnear and connected across the inner open ends of one of said cavityresonators, and means terminating the external portion of said line foradjusting the effective length of said line to control the operatingfrequency of said generator.

References Cited in the file of this patent UNITED STATES PATENTS2,084,867 Prinz et al June 22, 1937 2,144,222 Hollmann Ian. 17, 19392,163,589 Dallenbach June 27, 1939 2,167,201 Dallenbach luly 25, 19392,190,668 Llewellyn Feb. 20, 1940 2,242,404 Schussler May 20, 19412,243,426 Kircher May 27, 1941 2,348,986 Linder May 16, 1944 2,411,151Fisk Nov. 19, 1946 2,414,085 Hartman Ian. 14, 1947 2,435,984 SpencerFeb. 17, 1948

